Cellular structures in solid fuel combustion

Abstract

The objective of this contribution is to investigate whether the mechanism of the thermal diffusion instability in gaseous flames causing cellular flame structures also occurs during the combustion of porous solid fuel. Based on conservation for mass and energy, the relevant set of differential equations was derived. Assuming thermal equilibrium between fuel and oxidiser, a global energy equation was valid for both solid and gaseous phase. The resulting set of differential equations was discretised by the Collocation method to arrive at a system of algebraic equations. In order to investigate into cellular flame structures, an infinitesimal disturbance was superimposed onto the plane conversion front. Carrying out a linear instability analysis, yielded eigenvalues dependent on the wave number of the disturbance. A critical wave number exists below which the real part of the eigenvalues is positive, thus, indicating a regime of instability. Within this region, eigenvalues with a not-vanishing imaginary part of the eigen value existed causing cellular flame structures. However, the growth rate of disturbances was found to be small, which may explain the difficulty to investigate this phenomena experimentally.

Thermochemical Wear of Refractory Linings Associated With Gas Firing in Metallurgical Plants

“…Additionally the so‐called laminar flamelet concept can be used, which considers the local flame stretching and its further effect on conversion rate which follows from a turbulent dissipation of energy . The flamelet concept describes nonequilibrium phenomena in combustion chemistry and was already successfully implemented in previous studies . In the pre‐calculated flamelet lookup table species compositions are stored by stepwise increased strain rates up to a maximum where species conversions by all reactions in the combustion mechanism become zero.…”